1. Field of the Disclosure
The present invention is generally related to image sensors, and more specifically, the present invention is directed to high dynamic range image sensors.
2. Background
An image capture device includes an image sensor and an imaging lens. The imaging lens focuses light onto the image sensor to form an image, and the image sensor converts the light into electric signals. The electric signals are output from the image capture device to other components of a host electronic system. The electronic system may be, for example, a mobile phone, a computer, a digital camera or a medical device.
The demands on the image sensor to perform over a large range of lighting conditions, varying from low light conditions to bright light conditions are becoming more difficult to achieve as pixel cells become smaller. This performance capability is generally referred to as having high dynamic range imaging (HDRI or alternatively just HDR). High dynamic range imaging is a very desirable feature for a number of applications such as for example automotive and machine vision. In conventional image capture devices, pixel cells require multiple successive exposures such that the image sensor is exposed to both low and high light levels to achieve HDR. Traditional complementary metal oxide semiconductor (CMOS) image sensors suffer from low dynamic range due to limited well-capacity and fixed exposure times.
Corresponding reference characters indicate corresponding components throughout the several views of the drawings. Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various embodiments of the present invention. Also, common but well-understood elements that are useful or necessary in a commercially feasible embodiment are often not depicted in order to facilitate a less obstructed view of these various embodiments of the present invention.